This invention relates to short takeoff and landing aircraft, more particularly this invention relates to an automatic control system for enabling a short takeoff and landing aircraft to safely execute takeoff and landing procedures with one engine inoperative.
Several United States patent applications are related to the subject matter disclosed herein. They include Lewis et al., Ser. No. 339,734, filed Mar. 9, 1973, filed as a continuing, copending application Ser. No. 520,674, on Nov. 4, 1974; and now U.S. Pat. No. 3,977,630; Cole et al., Ser. No. 339,645, filed Mar. 9, 1973, now U.S. Pat. No. 3,837,601; and, Cole, Ser. No. 534,828, filed Dec. 18, 1974, and now U.S. Pat. No. 3,987,983 all of which are expressly incorporated herein by reference.
In the majority of presently proposed short takeoff and landing (STOL) aircraft, the aircraft is equipped with deployable control surfaces such as specially configured trailing edge flaps which can be deployed during STOL procedures to substantially increase the aircraft lift coefficient. During other flight regimes, such as cruise, these control surfaces are generally deployed in a manner which essentially places the aircraft in a more or less conventional aerodynamic configuration. In one type of STOL aircraft, which is particularly suited to the practice of this invention, augmentation of the aerodynamic lift that is supplied by the flow of the ambient air over the wing is effected by a technique identified as upper surface blowing (USB). In an aircraft utilizing upper surface blowing, the aircraft engines are mounted forwardly of and above the wings to discharge their exhaust stream chordwise across the upper airfoil surface of the wing. During normal flight, the exhaust stream is directed rearwardly to substantially generate forward thrust in a conventional manner. During STOL maneuvers, a type of trailing edge flaps, denoted herein as upper surface blown (USB) flaps, are employed to increase the camber and chord of the wing and at the same time form a continuously curved, downward and rearward extension of the upper airfoil surface of the wing. When the USB flaps are so extended, the exhaust stream traveling chordwise over the the upper airfoil surface of the wing attaches itself by the Coanda effect to the downwardly and rearwardly curved surface to divert the exhaust stream downwardly and rearwardly. In this manner, a lift component, as well as a forward thrust component, is generated by the exhaust stream. The engine-generated lift component augments the conventional aerodynamic lift created by ambient airflow over the remaining portion of the wing to provide a STOL capability.
As disclosed in the previously referenced copending applications, a serious problem is encountered when a STOL aircraft attempts to undertake a STOL landing or takeoff maneuver with one of the engines in an inoperative state, especially if loss of thrust occurs while the aircraft is engaged in the STOL maneuver. When this occurs, not only is the engine-generated forward thrust that is normally supplied by the inoperative engine lost, but the lifting force produced by flow turning over the USB flap is also lost. It should be noted that the terms "inoperative engine", "engine-out", and "engine failure", as utilized herein, are not limited to engine failure conditions under which an engine produces no thrust whatsoever. Specifically, as utilized herein, these terms encompass engine malfunctions in which an engine supplies an amount of thrust that is less than the amount selected by the aircraft commander or by an automatic flight control system, such lesser amount of thrust causing degradation of aircraft performance to the extent that short take off and landing maneuvers would be difficult to perform or even impractical.
USB flaps for partially alleviating the loss of lift caused by an inoperative engine by restoring some aerodynamic lift are disclosed in the aforementioned applications. These USB flaps generally comprise apparatus for reconfiguring the USB flap to a configuration that corresponds to that of a conventional slotted flap arrangement such as those used on many commercial aircraft to produce mechanical lift. In particular, each of the aforementioned applications disclose USB flaps wherein spanwise slots can be opened during an engine out condition such that ambient air can pass through the slots and produce mechanical lift to partially replace the lost engine-generated lift.
Although the USB flaps disclosed in the previously mentioned applications are operable to partially replace the loss of engine-generated lift, the use of such a flap alone often is not a satisfactory solution to the problem. First, it should be recognized that during a takeoff or landing procedure, the aircraft flight crew is performing under a substantial workload. Accordingly, it is desirable to restrict additional procedures to a minimum to thereby ensure the safety of the aircraft. Secondly, it should be recognized that under some engine failure conditions, little time is available for the aircraft commander to react. For example, if an engine fails while executing a short distance takeoff procedure, the aircraft commander may have less than 10 seconds to execute the control actions that are necessary in order for the aircraft to clear the end of the runway.
In addition to the problems that arise due to the physical limitations of the aircraft crew, the use of a USB flap without taking other appropriate control action does not place the aircraft in a desirable aerodynamic configuration. In particular, even though a portion of the engine-generated lift is restored by the spanwise slots that are opened in the USB flap, the distribution of lift across the upper surface of the aircraft wing will not be symmetrical and the airplane will have a tendency to roll. Although the aircraft commander could actuate various control surfaces, such as conventional spoilers or ailerons to reduce this rolling moment, such action not only increases crew workload but calls for judicious selection and operation of the proper control surfaces. In particular, less than optimal actuation of the control surfaces to alleviate the roll moment can cause a further increase in drag which can cause the aircraft to suffer a further loss in forward velocity or deteriorate flight path performance.
Accordingly, it is an object of this invention to provide a control system for automatically activating the control surfaces of a STOL aircraft to enable the aircraft to perform STOL maneuvers with an inoperative engine.
It is a further object of this invention to provide such a control system that does not substantially increase the workload placed on the aircraft commander, essentially allowing him to execute STOL procedures in the same manner regardless whether all engines are operative.